Regulation of photodynamic interactions in 1,8-naphthalimide-linker-phenothiazine dyads by cyclodextrins

Abstract

This study examines the effects of cyclodextrin (CD) on the photophysical properties of 1,8-naphthalimide (NI) derivatives including NI-linker-phenothiazine (NI-L-PTZ) dyads in a H2O/CH3CN solution (v/v = 9:1). Peculiar excimer and exciplex emissions were observed with reference NI and NI-L-PTZ, respectively, in an aqueous environment. The NI-CD complexes exhibited monomeric emission spectral features, which resulted from their inclusion into the CD cavity. The complex formation constants of CDs with the NI derivatives were determined. The T-1-T-n absorption band of (NI)-N-3* was observed at around 470 nm during nanosecond-laser flash photolysis. Photoinduced electron transfer in NI-L-PTZ led to NI center dot- and PTZ(center dot+) from the T-1 state. In protic polar solvents, NI center dot- easily formed a ketyl radical (NIH center dot) by hydrogen abstraction from H2O, and showed a transient absorption band at around 400 nm. The charge recombination (CR) time of the transient species at 400 nm showed a strong CD dependency, and the CR time of the dyad in gamma-CD was increased markedly compared with in beta-CD. This suggests that the PTZ moiety can also be included in the gamma-CD cavity.